[generator-macos] Enable auto-linking of native modules (#312)

* [generator-macos] Guard against package.json not having scripts yet

* [generator-macos] Enable auto-linking

Currently uses @react-native-communit/cli-platform-ios, but this is mostly
semantics as they work the same. In the future this will move into a
cli-platform-apple package which will hold common iOS and macOS tooling.

local-cli/generator-macos/index.js

@@ -134,8 +134,11 @@ function installDependencies(options) {
 
   // Patch package.json to have start:macos
   const projectPackageJsonPath = path.join(cwd, 'package.json');
+  /** @type {{ scripts?: {} }} */
   const projectPackageJson = JSON.parse(fs.readFileSync(projectPackageJsonPath, { encoding: 'UTF8' }));
-  projectPackageJson.scripts['start:macos'] = 'node node_modules/react-native-macos/local-cli/cli.js start --use-react-native-macos';
+  const scripts = projectPackageJson.scripts || {};
+  scripts['start:macos'] = 'node node_modules/react-native-macos/local-cli/cli.js start --use-react-native-macos';
+  projectPackageJson.scripts = scripts;
   fs.writeFileSync(projectPackageJsonPath, JSON.stringify(projectPackageJson, null, 2));
 
   // Install dependencies using correct package manager

local-cli/generator-macos/templates/macos/Podfile

@@ -1,7 +1,7 @@
-# require_relative '../node_modules/@react-native-community/cli-platform-ios/native_modules'
+require_relative '../node_modules/@react-native-community/cli-platform-ios/native_modules'
 
 abstract_target 'Shared' do
-  # use_native_modules!
+  use_native_modules!
 
   pod 'React', :path => "../node_modules/react-native-macos/"
   pod 'React-Core', :path => "../node_modules/react-native-macos/React"